The art of xerography, as originally disclosed by C. F. Carlson in U.S. Pat. No. 2,297,691, involves the uniform electrostatic charging of a plate comprising a conductive substrate having a uniform layer on its surface of a photoconductive material. Exposure of the charged surface to activating radiation in imagewise configuration causes the photoconductive material to become conductive in the irradiated areas whereby the charge is selectively dissipated leaving a latent electrostatic image corresponding to the non-exposed areas. The latent image is developed by contacting it with a particulate electroscopic marking material known as toner. In plain paper xerography, toner is transferred from the developed plate by contacting it with a sheet of paper which is subjected to an electrostatic charge opposite to that of the toner particles to thereby transfer at least part of the toner from the plate to the paper. After transfer, the toner is thermally fused into the paper to provide a permanent image. It is necessary in the toner transfer operation that the paper have a resistivity no greater than about 10.sup.13 ohms-cm. Paper having lower conductivity is likely to provide a poor copy, since it is necessary for a sheet adapted to the electrostatic reproduction of images to be an electrical conductor at the time the electrostatic charge is imposed on it prior to toner transfer. This requirement is a source of some difficulty in securing satisfactory performance with electrostatographic reproduction papers under different climatic conditions. It is also a source of difficulty in the use of certain papers with various types of copiers in which the paper sheets are automatically processed under conditions in which they are exposed to somewhat elevated temperatures in a dry atmosphere before and during the transfer of toner from the plate to the paper. When the paper is extremely dry, it will not properly accept the toner and to perform properly must contain at least about 2 percent by weight of water. Many theories as to the mechanism by which papers conduct electricity have been advanced but there is no generally accepted theory. It is, however, known that the electrical conductivity of the paper is dependent on its moisture content and upon the distribution of the moisture through the fiber structure, and that the conductivity is extremely sensitive to changes in the moisture content of the paper.
The addition of hydrated salts to paper to improve its conductivity is disclosed in U.S. Pat. No. 3,116,147. This patent discloses the addition of hydrated salts such as CaCl.sub.2.6H.sub.2 O, K.sub.2 CO.sub.3.2H.sub.2 O and LiCl .H.sub.2 O to paper to improve its conductivity under dry conditions. The use of a hydrated salt by itself is not a complete solution to the conductivity problem encountered during the copying procedure since the paper's conductivity is still somewhat humidity dependent. In addition, the deliquescent nature of many hydrates can result in over saturation of the paper under conditions of high humidity.
The problems encountered relating to paper dryness are especially noticeable in situations where copies are made in the duplex mode, i.e. where images are produced on both sides of the paper. Copying in the duplex mode causes problems in terms of low paper conductivity because the first fusing step drys the paper and renders it relatively non-conductive before it is subjected to the second copying procedure. This may occur even when the paper contains a hydrated salt since the salt will tend to lose its water of hydration at the temperature encountered during the first fusing step.
It would be desirable, and it is an object of the present invention, to provide a novel paper for use in electrostatographic copying.
A further object is to provide such a paper which provides improved performance in terms of reduced scorching and toner disturbances during the copying process.
An additional object is to provide such a paper which is especially adaptable to copying in the duplex mode.